Did some digging - his dad was a hitman who killed a Federal Judge who was tough on drugs/cartels.

"Known for his strict sentencing in drug trafficking cases, he was nicknamed "Maximum John". He was shot dead outside his home by contract killer Charles Harrelson, who was later convicted and sentenced to life in prison..."

Here's the guy who put him up to it: https://en.wikipedia.org/wiki/Jamiel_Chagra

So basically the dad shoots a judge who was about to throw the book at a big-time marijuana trafficker ('the biggest in the US') and then young woody begins to smoke so much weed it destroys his critical faculties. Guess payback is a bitch!